The trailing edge regions of turbine blades are often cooled by discharging spent cooling air through an array of holes or slots, which intersect and connect an internal cooling circuit and the external surface of the airfoil near the trailing edge region. The method of cutting back the pressure side to permit discharge of coolant to the pressure side of the airfoil is commonly referred to as “pressure side bleed”. In this system, cooling air is discharged from the pressure side, just upstream of the trailing edge, through an array of cooling holes, or ejection slots. The cooling holes are typically separated by solid features, which are hereinafter referred to as “riblets”. The current art includes riblets that form straight cooling passages and “diffusing” riblets that include an angle so that coolant can expand and spread to provide an increasing film cooling effect on the exposed trailing edge features. Examples of the current art can be found in U.S. Pat. No. 5,503,529, European Patent EP 1213442 and U.S. Pat. No. 5,246,341.
The current method of forming riblets typically involves a combination of casting and machining operations. The surface features inside the slot are typically a product of the casting process and are therefore called as-cast surfaces. The casting process typically leaves additional stock on the top of the lands, and also on the pressure side surface just forward of the pressure side bleed location. This material is typically removed following the casting process with both the aft pressure side and land top surfaces brought to the desired profile using an abrasive media.
With reference to FIGS. 1, 2A and 2B, an example of a turbine blade for a gas turbine engine illustrating such a cooling arrangement is indicated generally by the reference number 10. The blade 10 includes a plurality of ejection slots 12 and riblets 14 disposed along a trailing edge region of the blade. A conventional pressure side bleed slot geometry is illustrated in the enlarged views of FIGS. 2A and 2B. A problem to be solved involves cooling of the trailing edge region of a turbine blade using the pressure side bleed feature. In the current state of the art, coolant ejected from the pressure side bleed arrangement provides a cooling effect upon the surfaces contained within an ejection slot 12, while hot gas conditions from the pressure side of a blade and flowing along a pressure side surface 16 prevail on an upper or land surface 18 on the top of a riblet 14. Since the hot gas conditions exposed to the land surface 18 on the top of a riblet 14 can represent an extraordinary heat load, the ability to effectively cool the trailing edge region can be limited.
Accordingly, it is an object of the present invention to provide a turbine blade trailing edge configuration that overcomes the above-mentioned drawbacks and disadvantages.